According to the website, there is official Linux support, so no Proton at all, I suppose...

You can use these abbreviations with DNF too, by the way.

According to their website, they count public IP addresses hosting a list of services using shodan.

"We use data from the internet scanner Shodan.io, a search engine for publicly accessible servers. For each of the selected applications, we count the number of IP addresses per country that visibly run the software (based on html signatures and metadata)..." https://dsi.nextcloud.com/